Secondary emission means for gasfilled glow discharge character display tubes



April 25, 1967 TAISAKU KIZAKI SECONDARY EMISSION MEANS FOR GAS-FILLEDGLOW DISCHARGE CHARACTER DISPLAY TUBES Flled Sept 17 1963 InUEnT ORTaisa w K'lzaki FU'TOR IEY United States Patent 3,316,436 SECONDARYEMISSION MEANS FOR GAS- FILLED GLOW DISCHARGE CHARACTER DISPLAY TUBESTaisakn Kizaki, Mobara-shi, Chiba, Japan, assignor to Hitachi, Ltd.,Tokyo, Japan, a corporation of Japan Filed Sept. 17, 1963, Ser. No.309,477 Claims priority, application Japan, Sept. 20, 1962, 37/ 40,595 6Claims. (Cl. 313109.5)

The present invention relates to the structure of a gasfilled glowdischarge character display tube adapted for use with both alternatingcurrent and direct current.

Gas-filled glow discharge character display tubes (hereinafter referredto as CD. tubes) of conventional design comprise a common anode, atleast one metallic cathode, and a transparent vesselfor containing asuitable body of gas for maintaining negative glow, wherein individualcathodes are shaped in the form of respective numerals (0-9),alphabetical characters or special symbols. The structure of these C.D.tubes is such that, when a suitable positive voltage is impressed on theanode and a negative voltage is applied to the selected cathode, glow isgenerated from this specific cathode to display a desired character.When, however, a negative voltage is impressed on the anode and apositive voltage on the cathode, glow appears on the anode and it isimpossible to display the desired character. Therefore, the CD. tubes ofconventional design have not been adapted for use with the supply of anA.C. voltage.

The primary object of the invention is to provide a new and improvedC.D. tube operable on both A.C. and DC, which has a novel electrodestructure of such a feature that anodes and cathodes disposed in avessel are surrounded by a rare gas that can be ionized and a startingpotential of glow discharge at the anodes when supplied with a negativevoltage higher than the maximum value of A.C. voltage at which the CD.tube is operated.

According to the invention, there is provided a CD. tube comprising aclosed vessel filled with a rare gas that can be ionized, said vesselcontaining therein anodes, an electrode associated with said anodes, andat least one cathode, said anodes and said electrode associatedtherewith being subjected to a surface treatment by means such ascarbonization, oxidation or black chromium plating so that said anodesand said electrode associated therewith, which are at a negativepotential when said cathode is at a positive potential, have a startingpotential of glow discharge higher than the maximum value of A.C.voltage at which said C.D. tube is operated.

There are other objects and particularities of the invention which willbecome obvious from the following description with reference to theaccompanying drawing, in which the sole figure is a perspective view ofa preferred embodiment of a,C.D. tube according to the presentinvention, with portions broken away to show the internal structurethereof.

Referring to the drawing, there is shown .a transparent glass vessel 1in which a body of gas such as neon or argon at a pressure in the orderof several tens of mm. Hg is enclosed. A stem 2 is integrally joined tothe vessel 1 by means of fusion, and a plurality of base pins 3 ofmetallic material penetrate the stem 2 for providing electricalconnection with an external voltage supply source. Two pins 3' aredisposed diametrically opposite to each other and extend through thestem 2 into the vessel 1 to form supports 4 for supporting at least onecathode 5. Although not shown, the supports 4 are coated with a suitableinsulating material such as glass or the like. The cathode Sis made of asuitable metal such as stainless steel, iron, aluminium, Nicrome,molybdenum or the like and is formed into a shape of desired numeral,alphabetical "ice character or other special symbol by means such ascorrosion or punching. The cathode 5 has holes (not shown) boreddiametrically opposite to each other, by which any required number ofcathodes can be stacked in tiers on the supports 4 in suitably spacedrelation, with an insulating spacer 6 of steatite, multifoam glass orlike material interposed between the adjacent cathodes.

In order to provide electrical connection between each cathode 5 and thecorresponding base pin 3, a plurality of ribbons 7 of a suitable metalsuch as iron or nickel are secured to the cathodes 5 and the base pins 3as by electric spot welding. Surrounding the cathodes 5, there isprovided an anode 8 of a cup-like shape. Above said cup-like an'ode 8,there is also provided an anode 9 which is formed into a meshed screenshape to provide means of observing the glow. The mesh-like anode 9 isfirmly secured on the supports 4 by means such as caulking by eyeletgrummets 10 or electric spot welding, with the insulating spacers 6interposed between the anodes 8 and 9 to provide a suitable spacetherebetween. The cup-like anode 8 and the mesh-like anode 9 areelectrically connected with each other by a lead 11.

According to the invention, the electrodes 8, 9 and 11 forming theanodic elements of the CD. tube are made of a metal such as nickel, ironor aluminium, and are subjected to surface treatment by means such ascarbonization, oxidation or black chromium plating in order that astarting potential of glow discharge thereof is made higher than astarting potential of the cathodes 5 as well as a maximum value of A.C.voltage at which the OD. tube is operated. Thus, the surfaces of theanodic electrodes sotreated have extremely poor secondary electronemission than cleaned pure metal surfaces of the cathodes 5. Thecup-like electrode 8 is electrically connected to one of the base pins 3by a lead (not shown). Electrical insulation between the cup-like anode8 and the base pins 3 is provided by a plate 12 of an electricallyinsulating material such as mica.

Now, detailed explanation will be given hereinunder as to how the CD.tube of the invention with the above arrangement operates when suppliedwith alternating current. Generally, when ions of the rare gas enclosedin the vessel 1 approach the electrode surface to an extent of 2 to 3 A.therefrom, conduction electrons in the electrode transit to the groundstate of the ions which are thereby neutralized. Secondary electronemission will take place when electrons of another electrode aresupplied with the energy emitted during the above transition and finallymade to have higher energy than the potential barrier at the electrodesurface. Voltage impressed on the electrode in this case will appear asa starting potential of glow discharge.

As will be apparent from the foregoing description, the electrodes 8, 9and 11 forming the anodic elements of the CD. tube of the invention aremade to have an extremely poor degree of secondary electron emission bythe surface treatment. Therefore, the starting potential of glowdischarge of said anodic electrodes is apparently higher than a startingpotential of glow discharge of the cathodes 5 having cleaned pure metalsurfaces as well as a maximum value of A.C. voltage at which the CD.tube is intended for operation.

Further, when the CD. tube is energized by alternating current, glowwill be started at an instantaneous voltage. Therefore, a preferredarrangement may be such that the cathodes 5 are made to discharge andthe anodes are kept from discharging at a value /2 times the effectivevalue in the case of a sine wave.

Or more precisely, a relation of sine wave AC. voltage and the maximumvalue E thereof. When the starting potential of glow discharge of thecathode 5 is expressed as El and that of the anodes 8, 9 and the lead 11as E a relation E E exists as a,

result of said surface treatment. When a negative voltage is impressedon the cathode 5, glow discharge is developed at the cathode 5 due tothe relation E E, but when a negative voltage is likewise impressed onthe anodic elements comprising the anodes 8, 9 and the lead 11, glowdischarge will not take place at the anodic elements due to the relationE E. therefore that the purpose of the present invention can be attainedby the relation E E E When, for example, the CD. tube of the inventionis operated by sine wave alternating voltage at 100 volts,

and it will be readily known that E 130V and E l50 V will be quiteenough for the practical operation. It is needless to say that C.D. tubeof the invention can be equally effectively operated by direct current,as will be apparent from the above principle, in the manner in which ithas been operated heretofore.

What should be especially emphasized in the invention with regard to theoperation by alternating current is the necessity that all of the anodicelectrodes other than the cathodes '5 should be-so formed as to have thestarting potential of glow discharge higher than the maximum value ofA.C. voltage at which the CD. tube is operated. The surface treatmentapplied to the cup-like electrode 8 alone as in the case of conventionalC.D. tubes will not be effective to attain the excellent effect whichfrom the invention.

What is claimed is:

1. A glow discharge character display tube, comprising: a closed vesselcontaining an ionizable gas, anode means mounted within said closedvessel, said anode means including electrode means electricallyconnected to said anode, means, at least one cathode means mountedwithin said closed vessel in operable association with said anode means,individual ones of said cathode means each having a distinctive shape torepresent a predetermined character, said anode means and said electrodemeans having surfaces of lower secondary electron emission and higherstarting potentials of glow discharge than the surfaces of said cathodemeans such that when an alternating voltage results is applied betweensaid anode means and said cathode.

means a glow discharge is prevented from forming on said anode meansduring the alternate cycles of the alternating voltage when said anodemeans are negative with respect to said cathode means.

2. A gas-filled glow discharge character display tube according to claim1, wherein said surfaces of said anode means and said electrode meansare carbonized to produce a lower secondary emission than said cathodemeans.

It will be apparent.

3. A gas-filled glow discharge character display tube according to claim-1 wherein said surfaces of said anode means and said electrode meansare oxidized to produce lower secondary electron emission than saidcathode means.

4. A gas-filled glow discharge character display tube according to claim1, wherein said surfaces of said anode means and said electrode meansare plated with black chromium to produce a lower secondary emissionthan said cathode means. I

5. In a glow discharge character display tube having a closed vesselcontaining an ionizable gas, anode means and a perforated electrodemeans mounted within said closed vessel, said electrode means beingelectrically connected to said anode means, at least one cathode meansmounted within said closed vessel, in operable association with saidanode means and said electrode means, individual ones of said cathodemeans each having a distinctive shape to represent a predeterminedcharacter, the improvement essentially consisting of said anode meansand said electrode means having surfaces of lower secondary emissionthan the surfaces of said cathode means such that when alternatingvoltages are applied between said anode means, electrode means and saidcathode means, a glow discharge is prevented from forming on said anodemeans and said electrode means during the alternate cycles of thealternating voltage when said anode and said electrode means arenegative with respect to said cathode means.

6. A glow discharge display tube, comprising: a closed vessel containingan ionizable gas, anode means mounted Within said closed vessel, saidanode meansincluding electrode means electrically connected to saidanode means, at least one cathode means mounted within said closedvessel in operable association with said anode means, said cathode meanshaving a distinctive shape to represent a predetermined character,

means for applying an alternating potential between 'said anode meansand said cathode means, said anode means and said electrode means each'having surfaces of lower secondary emission and higher startingpotential of glow discharge than said cathode means.

References Cited by the Examiner UNITED STATES PATENTS 2,769,112 I10/1956 Heine et a1. 313-407 X 2,885,587 5/1959 Wainio et al. 313- 1072,930,919 3/1960 Wainio 313-409 2,996,635 8/1961 Klepp et al. 313- 109.5

v FOREIGN PATENTS 613,779 12/ 1948 Great Britain. 946,173 1/1964 GreatBritain.

JAMES W. LAWRENCE, Primary Examiner.

DAVID J. GALVIN, Examiner.

C. R. CAMPBELL, Assistant Examiner,

1. A GLOW DISCHARGE CHARACTER DISPLAY TUBE, COMPRISING: A CLOSED VESSELCONTAINING AN IONIZABLE GAS, ANODE MEANS MOUNTED WITHIN SAID CLOSEDVESSEL, SAID ANODE MEANS INCLUDING ELECTRODE MEANS ELECTRICALLYCONNECTED TO SAID ANODE MEANS, AT LEAST ONE CATHODE MEANS MOUNTED WITHINSAID CLOSED VESSEL IN OPERABLE ASSOCIATION WITH SAID ANODE MEANS,INDIVIDUAL ONES OF SAID CATHODE MEANS EACH HAVING A DISTINCTIVE SHAPE TOREPRESENT A PREDETERMINED CHARACTER, SAID ANODE MEANS AND SAID ELECTRODEMEANS HAVING SURFACES OF LOWER SECONDARY ELECTRON EMISSION AND HIGHER